Rare-earth metal fission products from liquid u-bi



"own fused halide. 7 I ties have been measured in systems of a salt in equilib- METAL FIssIoN PRODUCTS FROM LIQUID U -Bi- Richard H. Wiswall, Brookhaven, N.'Y., assignonto the United States of. America as represented by the United I States Atomic Energy Commission I No Drawing. "O'riginal applicatioh May 27, 1955, Serial N0. 511,810,:now 'Patent N0.'. 2,'840,464, dated June %..,..24,';1958. :-Divided and thisapplication February 19, ;1958,*Sel'lal N o. 716,253

3 Claims; (c1. 1s--s4.1

flThe present invention'relates'to aproces's for removing 7 metal selectively-fromliquid metal compositions. This application is a division of-my application, Serial Number It 'hasbeen proposed to produce heat-from fissionable.

-m'aterials'by dissolving themin liquid metal and exposing them'to'neutron irradiation. The fissionable metals-have low ,solubilityin liquid metal compositions having the 'neededcombinationof properties for use in connection with 'nuc'lear reactors and theyare therefore present-in such compositionsin low concentration. "One result of I [the irradiation 'oft'hese -"fissio'nable metals. by neutrons is the production of metallic and other fission-products -which remain in 'the liquid metal. -.'Ihe'concentration of fis'sion products is --low and should preferablybe kept at'a minimumin orderto prevent the wasteful-capture of neutrons; One process'fortheir removal is describedin 'Patent Number "2,758,023.; The present invention is an "improvement over that 'disclosed in the Bareis patent.

The capability of fused salts to act as solventsfor metals is'vvell known."- ItfisalSo known that the solubility may :bei'quite large as in the case of a metal dissolving in its Smaller, though significant, solubiliiium with a foreign metaL' The solbility of cadmium inmanganouschloride is an example. The distribution of metalibetweedsaltand metal is even less predictable if the metal is present incontact with the salt, not--in the V purestat'egbut in the form of a dilute solution in another" metal such as bismuth. If the behavior of metals in dilute solution in liquidmetal were that predicted for nitecl States Patent ice 2 is oxidizing with respect to a particularzmetal when the addition of the agent or halide to a liquid metal-liquid salt system, containing the particular metal, results in :the oxidation of the metal to form a halidew thereof. For

the purposes of this application if the particular ,metal is A-and its halide is AX and asecondmetal is'B and its halide is BX, the reaction occurring in the contacted liquid It has been discovered that the ratioof theconceintra- .tion of a particular-metal halide in a liquid halide composition, to the concentration of-the corresponding metal V in a-Jiquid metal composition, where the liquid halide :and liquid metal ;pl1ases are in Contactyis -ver'y'sensitive f I to changes in *the'degree of oxidation of the system;

When the metal and its halide are presen't' in relatively low concentrations in the two phases, transfer'of thelow concentration metal from solution in fthe'liquid' metal ,phase to the halide phase;may- .be acornplished by careful oxidation thereof, to ehfangegthe degree of oxidation of the ,system. This careful oxidation J-may be achieved by careful addition of an oxidizing agent to the contacted I f metal and halide-phases. a

.normal behavior in a solution, the ratio'of the'concentration of a particular metal inthe salt'phase, to its concentration in the metal phasew'ouldibe nearly, independent I of concentration. It has now be en discovered, however, -,jthat simple "solubility eflects do hot always govern the distribution of solute metals between a liquid metal'phase and" ailiquid salt phase 'in'corit'act therewith.

One offthe'objects ofithe present invention is to provr'de amore 'selective process for'the removal of' metals from liquid nietalcompositions. Another object-is to provide a method- 'forTremoving low concentrations of metals'f rom solution in liquid-metal media. -Afur'ther object is to provide a method for selectively removing metals individually from {a group of:metals in solution in a liquid metal medium; Other objects; will be in part apparent and inpart' pointedxouthereinafter.

' In one ofits broader aspects, the objects of'the-present invention are achieved by dissolving/the metals- "to be "Separated [in a'liquid metal ,compositionfforming a'fu'sed halide composition containin'ghalides of metals which are reducingwith respect to thehalides of the metals of said 3 composition, contacting said liquid metal and halide compositions, adding to sjaidcompositions an agent capable j of' oxidizing the metal to be removed and separating'the' halide and metal phases.

-- t cr'permit the .oxidation of a particular-metalselectivel {for the purposes ofthis application an agentorahalide' at the 1 'fluidebe decreases with increasing temperature.

' Ihave found that a-nearlyquantitative-transferiof low concentration metal occurs following the oxidation, al-

though the free energy of formation of its halide-is only slightly different from that of other metals present-in the liquid metal'iphase. The following expression is useful in relating the concentrations of metals and their halides in a :two phase liquid-metal, liquid-halide system:

In this, expression and are the concentrations of the metals-in the liquid: phase and AX and BX are the concentrations of the halides of these metals in the halide, phase. For aparticular pair of metals and-their halides the.- ratioR is approximately constant; thatjis,=it is nearly findependentof the absolute valuesi-of the concentrations if-these, are small. For a. system of ,metals;.and -their halide :salts; th'e value of R is very sensitiveto .diiferences v i Q in .the .stabilities or free'energies of formation of the halides. It 'has been found that the value of 'R for two .metal chlorides, which differ in' their .free energies'of formation by approximately. 10 kilocalories perjgram atom of chlorine contained, is about 1000 at about750 I K. Ifthe two metals, A and B, are present in a liquid metal-liquid salt composition in the metal state, and. the

diflference in free'energies of formation of their chlorides is as little as 10 k'ilocalories per gram atom of chlorine contained, the addition of oxidant results in a nearly quantitative transfer of themetal formingthe'moregstable chloride to the salt phase. The separation of two :metal halides having smaller differences in their 'free energies of formation, as small as 4 kilocalor'ies .per gram atom of chlorine contained, is feasible by the present method faltlrough the separation achieved. as a result; ofia single oxidation as noted above, is not as complete. i'separationis possible at the'lower difi'erence in free energy it is preferred to carry out thepresent' method owest temperature at which the materials. are i cause the separation factor, i.e., thevalue of 1B,;

Thetliquid metaland 'alt compositions may belcho sen fromother' inetals prescntin low concentrations and tlre 7 2,936,231. Patented May -16,1960

" A ten fold i transfer thereof between phases. Where two metals are to be separated, a solvent metal capable of dissolving both of them is chosen and the liquid metal composition containing the metals to be separated as solute, is contacted with a fused metal composition containing halides of metals which are more stable than the metals of the liquid metal composition. An oxidizing agent is then added to selectively oxidize one of the solute metals to form a halide. Following the oxidation, the formed halide transfers to the liquid salt phase and by separating the liquid salt and liquid metal phases, the two metals are separated.

The method of the present invention may be illustrated with reference to the removal of fission product metals from solution in liquid bismuth containing uranium dissolved therein. Uranium is soluble at a concentration of approximately a few tenths of a percent in liquid bismuth at temperatures between 400 and 600 C. The irradiation of this solution in a neutron flux results in the formation of fission product metals such as cesium, barium and the rare earth metals. The concentrations in which these metals are formed depends on the neutron flux in the bismuth, the length of time of exposure and the frequency of fission product removal. Concentrations may range between one part per billion to about 1%.

It has been found possible to remove these fission product metals selectively from solution in liquid bismuth without removal of an appreciable quantity of uranium by contacting the liquid metalsolution with fused halides, as for example, the halides of sodium, potassium and lithium, and by adding to the contacted phases a quantity of a halide which is unstable relative to the halides of the fission products noted above. Removal of approximately 90 to 95% of these fission products to the liquid salt is accomplished in this manner.

One oxidizing agent which is particularly useful in this connection is bismuth chloride. Bismuth chloride is an unstable halide relative to the stability of some fission product metal halides such as the rare earth halides. Bismuth chloride is also more unstable than uranium chloride and its addition must be limited to the quantity stoichiometrically equivalent to the quantity of the metals present which form more stable halides than uranium. The addition of the stoichiometric quantity is necessary to avoid transfer of appreciable quantities of uranium to the liquid salt as uranium chloride. About 90% of such fission products can be transferred Without transferring more than one percent of the uranium. In the absence of uranium transfer of the metal fission products forming more stable halides than bismuth chloride can be accomplished by adding to the contacted liquid phases a quantity of bismuth chloride stoichiometrically equivalent to the quantity of such fission products present in the metal. Transfer of rare earth fission products from liquid metal to liquid salt can also be accomplished by additions of other metal halides such as lead, zirconium, manganese and aluminum. When bismuth is the liquid metal solvent, the particular virtue of bismuthchloride is that the bismuth produced becomes part of the solvent metal and thus does not introduce any foreign material into the liquid metal composition.

Although the fission product metals are present in very small concentrations, it is possible to selectively and individually remove those of the metals having appreciable differences in stability, i.e., more than kilocalories per gram atom of chlorine contained, from solution in liquid metal by discrete additions of oxidizing halides in 'quantities stoichiometrically equivalent to the quantity of the individual fission products to be removed. The separation of such fission products is very desirable because of their different radiation properties. For example, the pure radiation product, cesium, is considered veryvaluable because of its utility in medical radiation treatment. As metals are separated from a group of metals dissolved in a liquid metal medium and transferred to a halide salt, it is desirable to remove the halide of the transferred metal from the liquid salt composition. For this purpose salt to which a particular component has been transferred as a halide may be separated from the first liquid metal and placed in contact with a second liquid metal composition, a reducing agent added to the newly contacted materials to cause a reduction of the particular halide and its transfer to the second liquid metal.

It has further been found that the fission product metals, particularly the rare earths, can be continuously removed from bismuth by contacting the metal with a salt of a composition providing an oxidation buffer. For this purpose, the salt composition itself should preferably contain a component halide capable of continuously oxidizing the fission product metals as they are formed and the liquid metal compositions must contain a quan tity of the metal of this component halide. With regard to the oxidizing component halide, it should preferably be intermediate in its stability between the halides of the metals to be retained in the metal phase and the halides of the metals to be removed to the salt phase. In order to maintain an oxidation buffer system, the metal of the oxidizing halide must also be present in the liquid metal.

One example of this is the continuous removal of rare earth fission product metals from a liquid bismuth composition, without removal of significant quantities of uranium, by maintaining magnesium metal present in the bismuth and magnesium chloride present in the salt, and by maintaining the ratio of the concentration of magnesium chloride present in the salt to the concentration of magnesium metal presentin the metal phase at a value of about 5000. For this purpose, a salt containing 18% KCl, 2.4% NaCl, and 58% MgCl may be employed. The preferred concentration of magnesium in the metal phase of about parts per million or 0.01%, is maintained in order to keep the value of the ternary salt-tometal concentration ratio MgCl /Mg, at about a value of 5000.

One advantageous result made possible by the present method is the separation of metals from metal solution although the dissolved metal is present in solution in extremely small quantities. Where appreciable solubility of the metal in the fused salt exists, the method is not useful in separating comparably small quantities of metals from solution. In one of its broader aspects, the method includes the removal of metal from metal solution by dissolving the metals in a base metal of low halide stability, contacting the metal solution with a fused halide of high halide stability and oxidizing the less noble metal to a salt in order to selectively remove metal from solution.

The use of fluorides and other halides in place of chlorides is contemplated Within the scope of the present method. For example, in some systems, a metal bromide, such as, magnesium bromide, may be used to advantage.

Since many embodiments might be made ofthe present invention, and since many changes might be made in the embodiment described it is to be understood that the foregoing description is to be interpreted as illustrative only and not in a limiting sense.

I claim: I p

1. The method of separating at least some of the metal fission products of uranium from solution in a liquid bismuth composition containing uranium without removing the uranium therefrom which comprises contacting said liquid bismuth composition with a fused chloride composition containing approximately 58% magnesium chloride, 18% sodium chloride and maintaining in saidliquid bismuth composition a magnesium metal concentration of approximately 100 parts per million and thereafter separating said liquid bismuth composition from said fused chloride composition.

2. The method of continuously removing rare earth .metal fission products of uranium from solution in a potassium chloride and 24%- liquid bismuth composition, without causing removal of more than 1% of uranium metal also dissolved therein, which comprises contacting said liquid bismuth composition with a fused salt composition containing 18% KCl,

' 24%, NaCl and 58% MgCl maintaining a magnesiummetal concentration in said liquid bismuth of about 100 parts per million and separating the liquid bismuth from contact with said fused salt composition.

- corresponding chloride of said fission product metals and which is relatively more stable than uranium chloride,

said chloride being selected chlorides, maintaining in said liquid bismuth, a small proportion of, and relative to, the metalt of said selected metal chloride to prevent transfer of said uranium to the liquid bismuth and thereafter separating the said contacted fused chloride from the liquid bismuth composition.

References Cited in the file of this patent UNITED STATES PATENTS 2,758,023 r Bareis Aug. 7, 19 56 2,840,4641. Wiswall June 24,1953

y from the group consistiugof bismuth, lead, zirconium, manganesejand aluminum UNITED STATES P'ATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,936,231 May 10 1960 Richard H, Wiswall It is hereby certified that error appears in the above numbered patent requiring correction and that the; said Letters Patent should read as corrected belown In the heading to the printed specification lines 2 and 3 title of invention, for "RARE-EARTH METAL FISSION PRODUCTS FROM LIQUID U-Bi" read SEPARATION OF RARE-EARTH METAL FISSION PRODUCTS FROM LIQUID U-Bi Signed and sealed this 20th day of December 1960.

(SEAL) Attest:

KARL H. AXLINE Atte sting Officer ROBERT WATSON Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIDN Patent No, 2336 231 May 10 1966 Richard H. Wiswall It is hereby certified that error appears in the above numbered patent requiring correction and that the.- said Letters Patent should read as corrected below.

In the heading to the printed specificatiom lines 2 and 3 title of invention, for "RARE-EARTH METAL FISSION PRODUCTS FROM LIQUID U-Bi" read SEPARATION OF RARE-EARTH METAL FISSION PRODUCTS FROM LIQUID U-Bi Signed and sealed this 20th day of December 1960a (SEAL) Attest:

KARL H, AXLINE Attesting Officer ROBERT WATSON Commissioner of Patents 

1. THE METHOD OF SEPARATING AT LEAST SOME OF THE METAL FISSION PRODUCTS OF URANIUM FROM SOLUTION IN A LIQUID BISMUTH COMPOSITION CONTAINING URANIUM WITHOUT REMOVING THE URANIUM THEREFROM WHICH COMPRISES CONTACTING SAID LIQUID BISMUTH COMPOSITION WITH A FUSED CHLORIDE COMPOSITION CONTAINING APPROXIMATELY 58% MAGNESIUM CHLORIDE, 18% POTASSIUM CHLORIDE AND 24% SODIUM CHLORIDE AND MAINTAINING IN SAID LIQUID BISMUTH COMPOSITION A MAGENSIUM METAL CONCENTRATION OF APPROXIMATELY 100 PARTS PER MILLION AND THEREAFTER SEPARATING SAID LIQUID BISMUTH COMPOSITION FROM SAID FUSED CHLORIDE COMPOSITION. 